Collimators and collimator arrays employing ellipsoidal solid immersion lenses

ABSTRACT

An ellipsoidal solid immersion lens (ESIL) for use as a collimator for a waveguide. The ESIL has a refractive index n, an ellipsoidal surface portion defining a geometrical ellipsoid with geometrical foci F 1 , F 2  along a major axis of length M. The ESIL has an attachment surface portion for joining to the waveguide. The attachment surface portion passes near or through the second geometrical focus F 2 . The geometrical foci F 1 , F 2  are separated by a distance S =M/n, such that a substantially collimated light beam exhibiting a Gaussian type intensity profile propagating along the major axis M and entering the ESIL through the ellipsoidal surface portion converges to a Gaussian beam waist substantially at the attachment surface portion. The ESIL, or more generally any SIL, may be incorporated into a collimator array within a monolithic body having a substrate with a substantially uniform index of refraction and a plurality of pedestals comprising attachment surface portions for attaching waveguides to the respective SIL&#39;s.

RELATED APPLICATIONS

This application is a continuation-in-part of application 09/698,993filed on Oct. 27, 2000. Application 09/698,993 filed on Oct. 27, 2000 isa continuation-in-part of U.S. Pat. Application No. 09/354,841, filedJul. 16, 1999, now U.S. Pat. No. 6,181,478, issued Jan. 30, 2001.

FIELD OF INVENTION

This invention generally relates to solid immersion lenses andcollimators using such solid immersion lenses.

BACKGROUND OF THE INVENTION

In many optical systems and applications, such as near-field microscopy,imaging, photolithography and optical storage it is important to reducethe spot size and thus obtain higher definition or resolution. The spotsize of an optical system, e.g., an optical storage system, is commonlydefined as the distance between half power points. This distance isdetermined by diffraction to be approximately λ/(2·NA), where λ is thefree space wavelength of the light used and NA is the numerical apertureof the objective lens focusing the light beam. NA is defined asNA=nsin(θ), where θ is the half cone angle of the focused light rays andn is the index of refraction of the medium in which θ is measured.

One way to improve the definition is to work at shorter wavelengths λ,e.g., in the green or blue range, and to increase the numerical apertureto be as close to one as possible. A further possibility is to employnear-field optics in the manner described by Betzig et al. in AppliedPhysics Letters, Vol. 62, pp. 142 (1992), using a tapered fiber with ametal film with a small pinhole at the end. The definition of the systemis determined by the size of the pinhole, and can be 50 nm or less. Theadvantages of the fiber probe system are its excellent definition andits polarization preserving capability which is particularly useful inmagneto-optic storage applications. The disadvantages of the system areits poor light efficiency and the fact that it can only observe a singlespot at a time, thus limiting its tracking ability when used for opticalstorage.

Another alternative is to use a solid immersion lens (SIL) between theobjective lens and the illuminated object, e.g., an optical recordingmedium or sample under investigation. The SIL is placed within awavelength λ or less (in the near-field) of the object. Optical systemstaking advantage of appropriate SILs are described, e.g., by S. M.Mansfield et al. “Solid Immersion Microscope”, Applied Physics Letters,Vol. 57, pp. 2615-6 (1990); S. M. Mansfield et al. “High NumericalAperture Lens System for Optical Storage”, Optics Letters, Vol. 18, pp.305-7 (1993) and in U.S. Pat. No. 5,004,307 issued to G. S. Kino et al.In this patent Kino et al. teach the use of a high refractive index SILhaving a spherical surface facing the objective lens and a flat frontsurface facing an object to be examined. The use of this SIL enables oneto go beyond the Rayleigh diffraction limit in air. In one embodiment,the SIL is employed in a near-field application in a reflection opticalmicroscope to increase the resolution of the microscope by the factor of1/n, where n is the index of refraction of the SIL.

A paper by G. S. Kino presented at the SPIE Conference on Far- andNear-Field Optics, “Fields Associated with the Solid Immersion Lens”,SPIE, Vol. 3467, pp. 128-37 (1998) describes in more detail theprinciples of operation of two particular SILs. The first is ahemispherical SIL and the second is a supersphere SIL or a stigmaticSIL. The hemispherical SIL improves the effective NA of the objectivelens by the refractive index n of the SIL and decreases the spot size by1/n. The supersphere SIL increases the effective NA of the objectivelens by the square of the refractive index n² and obtains a focus at adistance a/n from the center of the supersphere, where a is the sphere'sradius. The spot size is reduced by a factor of n². The performancecharacteristics and theoretical limitations of both types of SILs arealso discussed.

SILs have found multiple applications. For example, Corle et al. in U.S.Pat. No. 5,125,750 teach the use of a SIL in an optical recording systemto reduce the spot size in an optical recording medium. These SILstypically have a spherical surface facing the objective lens and a flatsurface facing an optical recording medium. The flat surface is in closeproximity to the medium.

In U.S. Pat. No. 5,497,359 Mamin et al. teach the use of asuperhemisphere SIL in a radiation-transparent air bearing slideremployed in an optical disk data storage system. Lee et al. in U.S. Pat.No. 5,729,393 also teach an optical storage system utilizing a flyinghead using a SIL with a raised central surface facing the medium. InU.S. Pat. No. 5,881,042 Knight teaches a flying head with a SILpartially mounted on a slider in an optical recording system. Thisslider incorporates the objective lens and it can be used in amagneto-optic storage system. Finally, in U.S. Pat. No. 5,883,872 Kinoteaches the use of a SIL with a mask having a slit for further reducingthe spot size and thus increasing the optical recording density in anoptical storage system, e.g., a magneto-optic storage system.

The prior art SILs as well as the optical systems using them have anumber of shortcomings. Hemispherical SILs suffer from back reflectionproblems. These degrade system performance, especially when the lightsource is a laser, e.g., a laser diode, and the back reflection iscoupled back into the laser. Also, the ray reflected from the sphericalsurface and the ray reflected from the flat surface or from an objectjust below the flat surface are coincident. This gives rise toundesirable interference effects.

Superhemispherical SILs have reduced back reflection. However, theydemagnify the image of the object by a larger factor than hemisphericalSILs. For example, the demagnification of superhemispherical SILs in theaxial direction is 1/n³. Because of this, the length tolerance for thesuperhemispherical SIL is very tight. Both the hemispherical andsuperhemispherical SILs increase the effective NA (NA_(eff)) of theobjective lens (for hemispherical SIL NA_(eff)=NA_(objective)·n; and forsuperhemispherical SIL NA_(eff)=NA_(objective)·n²). The maximum NA_(eff)that can be obtained by either type of SIL is NA_(eff)=n.

Hemispherical, superhemispherical and related SILs experience alignmentproblems because optical systems employing them require the use of aseparate objective lens. This separate lens has to be accurately alignedwith the SIL. In many optical systems alignment between these two lensescannot be easily preserved due to external influences (vibrations,stresses, thermal effects etc.). In addition, in systems where thenumber of parts is to be small, e.g., for weight and size reasons theobjective lens is cumbersome.

Also it is well known in the art that a plurality of lenses (ormicro-lenses) can be fabricated within a monolithic body in an orderedarrangement to comprise a lens array (or micro-lens array). Such lensarrays may be formed by processes that include photolithography,etching, ion milling, reflowed photoresist methods, molding, and thermalbonding methods as described in Optics & Photonics News, Sep. 1999, pp.19-22, and in “Microoptics”, by Stefan Sinzinger and Jurgen Jaohns,Wiley-VCH, 1999. Unfortunately, the arrays disclosed in the prior art donot effectively overcome the difficulties associated with attachingmultiple waveguides to a monolithic body in precise alignment with thecorresponding lenses.

In addition, there is a need in the industry to develop effective,light-weight and easy to use collimators for waveguides such as opticalfibers. The fusing of lenses, e.g., graded index lenses (GRINs), to theends of fibers is known and described, e.g., in U.S. Pat. No. 4,737,006to Warbrick, U.S. Pat. No. 4,962,988 to Swann and U.S. Pat. No.6,033,515 to Walters et al. These patents also teach techniques forperforming fusion splicing of a lens to the fiber. Additional fusionsplicing techniques are described, e.g., in U.S. Pat. No. 5,299,274 toWysocki et al. and U.S. Pat. No. 5,745,311 to Fukuoka et al. These andother prior art fusion spliced parts and splicers attempt to overcomealignment problems encountered in these techniques.

Unfortunately, prior art SILs require additional objective lenses, asmentioned above, and require precise alignment with those. Hence propersplicing with a waveguide, e.g., a fiber, is only one of the problems.Monolithic arrays further increase the difficulties associated withproper alignment as multiple waveguides must now be precisely alignedwith each SIL. It would be an advance in the art if SILs and SIL arrayswhich are less tolerant to alignment problems could be developed forfusion splicing with waveguides and advantageously used to collimate therespective diverging beams of light emerging from the waveguides. Itwould also be an advance in the art to develop micro-SIL arrays forrespectively collimating the diffraction-limited Gaussian beams emergingfrom a large number of single-mode optical fibers arranged in a highdensity packaging configuration (fiber array).

OBJECTS AND ADVANTAGES

Accordingly, it is a primary object of the present invention to providea solid immersion lens (SIL) which overcomes the prior art limitationsand ensures a small spot size. It is a specific object of the inventionto integrate the objective lens and the solid immersion lens into asingle collimator.

It is a further object of the invention to provide such an integratedSIL for fusion splicing applications with waveguides such as opticalfibers. Additionally, it is a specific object of the invention toprovide means for reinforcing the attachment of waveguides to the SILs.

It is another primary object of the invention to provide a monolithicarray which overcomes the prior art shortcomings in precisely aligningattached waveguides.

Further objects and advantages will become apparent upon reading thedetailed description.

SUMMARY

The objects and advantages of the invention are secured by a collimatorintegrated with a waveguide and employing an ellipsoidal solid immersionlens (ESIL). The ESIL has a substantially uniform index of refraction n,an ellipsoidal surface portion defining a geometrical ellipsoid with amajor axis M, a first geometrical focus F₁ and a second geometricalfocus F₂ separated from first geometrical focus F₁ by a separationS=M/n. The collimator has an attachment surface portion passingsubstantially through second geometrical focus F₂. The attachmentsurface portion is for attaching the ESIL to the waveguide such that acollimated light beam propagating along major axis M through theellipsoidal surface portion converges to a focus substantially at secondgeometrical focus F₂ or at the waveguide.

The attachment of the attachment surface to the waveguide can beperformed in many ways. The manner in which the waveguide and ESIL arejoined can be adapted to the type of waveguide, e.g., an optical fiberor a buried waveguide. In one embodiment the attachment surface isattached to the waveguide by a fused butt joint.

In one convenient embodiment of the invention the ESIL has a body and apedestal. The body has the ellipsoidal surface portion through whichlight passes. The pedestal has the attachment surface portion by whichthe ESIL is attached to the waveguide. The pedestal can have a pedestalcross section dimensioned to match the waveguide. For example, when thewaveguide is an optical fiber the pedestal cross section can equal thatof the optical fiber. The pedestal cross section can also be tapered,e.g., it can be tapered down from a larger cross section to the crosssection of the waveguide at the attachment surface portion. In anotherembodiment the ESIL has a cross section matched to the waveguide.

The ESIL, or more generally any SIL, can further be integrated into amonolithic body. The substrate of this monolithic body allows formultiple SILs to be combined in one body. A monolithic bodyincorporating an array of SILs can be formed using photolithography,etching, ion milling, reflowed photoresist methods, molding, or othercommon processes. A useful embodiment of the invention has pedestals onthe attachment surface portion of the substrate to provide for low-losscoupling and increased precision in attaching waveguides, resulting inimproved pointing accuracy of the collimator. A reinforcing structuremay also be employed to stabilize the attachment of waveguides to themonolithic body.

The ESIL can be made of one or more sections, depending on theapplication of the collimator and design requirements. However, it ispreferable that the attachment surface portion be flat for easierattachment, e.g., by fusion bonding to the waveguide.

The details of the invention are explained in the detailed descriptionin reference to the attached drawing figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a cross sectional side view of an optical system employing anESIL according to the invention.

FIG. 2 is a detailed schematic view of the ESIL of FIG. 1.

FIGS. 3A-D are cross sectional side views illustrating variouscollimators employing ESILs according to the invention.

FIG. 4 is a cross sectional side view of an optical system employing twoESILs with a collimated Gaussian beam as described by the invention.

FIG. 5 is an orthographic view of multiple SILs arranged in a monolithicbody.

FIGS. 6A-D are cross sectional side views illustrating collimatorsemploying multiple SILs according to the invention.

FIGS. 7A-B are cross sectional side views of reinforcing structures asdescribed by the invention.

DETAILED DESCRIPTION

FIG. 1 illustrates in a cross-sectional side view a general opticalsystem 10 employing an elliptical solid immersion lens (ESIL) 12 with anellipsoidal surface portion 14. System 10 has a light source 16 whichdelivers a diverging light beam 18. A collimating lens 20 is placed inthe path of beam 18 to form a collimated light beam 22.

Collimated beam 22 passes through a beam splitter 24 and is incident onthe ellipsoidal surface portion 14 of ESIL 12. ESIL 12 is made of asuitable refractive material, e.g., glass or plastic, having asubstantially uniform index of refraction n. ESIL 12 is mounted in asupport plate 28. Plate 28 can be made of the same material as ESIL 12or a different material.

In fact, ellipsoidal surface portion 14 defines an entire geometricalellipsoid 26. The remaining portion of geometrical ellipsoid 26 beyondactual ESIL 12 is drawn in dashed lines. Ellipsoid 26 has a major axis Mas well as a first geometrical focus F₁ and a second geometrical focusF₂. Both geometrical foci F₁, F₂ lie on major axis M.

ESIL 12 has a flat interface surface 30 which passes through secondgeometrical focus F₂ of ellipsoid 26 such that geometrical focus F₂itself is contained inside ESIL 12. Interface surface 30 should be asclose as possible to F₂ for best performance. A height h of ESIL 12 isthus defined between interface surface 30 or geometrical focus F₂ and avertex V₁, at the top of ellipsoidal surface portion 14.

Interface surface 30 of ESIL 12 is positioned a distance g above anobject 32. Distance g is set at less than a wavelength λ of light makingup beam 22. In other words, object 32 is placed in the near-field regionof ESIL 12.

In this embodiment, object 32 is a sample to be examined optically inregion 33 of interest. Optical system 10 is a microscope set up toreceive a light beam 34 back-scattered or reflected by object 32 uponillumination with beam 22. Back-scattered or reflected beam 34 passesback through ESIL 12 and is deflected by beam splitter 24 and focused bya lens 36 to a detector 38. Advantageously, system 10 employs theprinciples of confocal microscopy well-known in the art.

The operation of ESIL 12 will be better understood by examining FIG. 2in which geometrical ellipsoid 26 is shown in cross section along majoraxis M. The cross section of ellipsoid 26 is an ellipse 40; ellipsoid 26is generated by revolving ellipse 40 around major axis M. Ellipse 40 isdefined in accordance with standard geometrical conventions. Inparticular, ellipse 40 is defined with the aid of a first directrix D₁and a second directrix D₂ as follows:

{overscore (PF)} ₁ =e{overscore (PD)} ₁

and

{overscore (PF)} ₂ =e{overscore (PD)} ₂

where {overscore (PF)}₁, {overscore (PD)}₁, {overscore (PF)}₂ and{overscore (PD)}₂ represent the distances shown in FIG. 2 between pointP and focus F₁, directrix D₁, focus F₂ and directrix D₂, respectively,and where e is the eccentricity of ellipse 40. Eccentricity e is definedas: ${e \equiv \frac{c}{a}} = {\frac{\sqrt{a^{2} - b^{2}}}{a}.}$

The distance from the center O of ellipse 40 to either focus F₁, F₂ is cand a separation S between foci F₁, F₂ is thus equal to 2c (S=2c). Thelength of major axis M is equal to 2a and the distance betweendirectrices D₁, D₂ is equal to M/e.

In accordance with the invention, refractive index n of ESIL 12 isselected such that separation S between foci F₁, F₂ is equal to thelength of major axis M divided by refractive index n, in other wordsS=2c=M/n. Under this condition collimated light beam 22 propagatingparallel to major axis M and entering ESIL 12 through ellipsoidalsurface portion 14 is focused at second geometrical focus F₂. Also,light 34 back-scattered at geometrical focus F₂ returns through SIL 12along the path traversed by beam 22. In fact, light 34 back-scattered innear-field region 33 of geometrical focus F₂ returns substantially alongthe same path as beam 22 and is used for imaging object 32. Bothevanescent and plane waves can be involved in the back-scatteringprocess. For a theoretical description of the fields in the near-fieldregion of a SIL see G. S. Kino, SPIE Conference on Far- and Near-FieldOptics, “Fields Associated with the Solid Immersion Lens”, SPIE, Vol.3467, pp. 128-37 (1998).

It will be appreciated by a person skilled in the art that the presentdesign of ESIL 12 integrates the function of objective lens and the SILas used in prior art systems. In other words, ESIL 12 is actually anintegrated objective and SIL lens. The effective NA, NA_(eff), and themaximum effective NA, max. NA_(eff), can both be expressed in terms ofindex n of ESIL 12 as follows: NA_(eff) = n  sin   θ${\max \cdot {NA}_{eff}} = {{n\quad \sin \quad \theta_{M}} = \sqrt{n^{2} - 1}}$

The design parameters of ESIL 12 are advantageously expressed in termsof refractive index n. Table 1 gives the design parameters for severalparticular choices of index n of ESIL 12. The design parameters areexpressed in terms of n as well as in terms of lengths a, b andeccentricity e.

TABLE 1 {square root over (n² − 1)} {square root over (n² − 1)}/n 1/nλ/2 · NA_(eff) n max. NA_(eff) b/a e spot size at λ = 400 nm 1.5 1.118.745 .667 170 nm 2.0 1.732 .866 .500 115 nm 2.5 2.291 .917 .400 87 nm3.0 2.828 .943 .333 70 nm 3.5 3.354 .958 .286 59 nm

Although in the above embodiment ESIL 12 is used in microscope 10 it canbe implemented in any other optical system requiring small spot size,high resolution and mechanical stability obtained by virtue ofeliminating the objective lens. Specifically, ESIL 12 can be used as acollimator for waveguides such as optical fibers or buried waveguides.

FIG. 3A illustrates an ESIL 50 according to the invention with anattachment surface portion 52, which is also the interface surfaceportion passing through or very near second geometrical focus F₂ of ESIL50. ESIL 50 has an ellipsoidal surface portion 58, which is smaller thanin the previous embodiment, and defines a geometrical ellipsoid 60. Asbefore, ellipsoid 60 has a major axis M along which lie the two foci F₁,F₂ at the separation governed by S=M/n.

In this embodiment ESIL 50 is a collimator integrated with a waveguide54, in this case an optical fiber, by a fused butt joint 56 atattachment surface portion 52. ESIL 50 has a body 62 which terminates atellipsoidal surface portion 58. Body 62 has a side wall 66 and a flatbottom 64 opposite ellipsoidal surface portion 58. It will beappreciated by a person skilled in the art that the exact shape of sidewall 66 and bottom 64 are a matter of the designer's choice as long as acollimated light beam 68 propagating along major axis M throughellipsoidal surface portion 58 converges to an optical focus at secondgeometrical focus F₂. In other words, the design of body 62 should notinterfere with the propagation of light 68 through body 62.

A cylindrical protrusion or pedestal 70 extends from bottom 64 of body62. It is important that the region between body 62 and pedestal 70preserve a uniform refractive index n. To ensure this body 62 andpedestal 70 can be molded as one part out of moldable glass or plasticor produced at the same time by a photolithographic technique. Forfurther information on photolithographic and other fabricationtechniques which can be used in the manufacture of ESIL 50 see, e.g.,Optics & Photonics News, Sep. 1999, pp. 19-22, and in “Microoptics”, byStefan Sinzinger and Jurgen Jahns, Wiley-VCH, 1999.

Pedestal 70 has a cross section 72 which closely matches a cross section74 of optical fiber 54. This matching of cross sections provides forboth parts having a similar thermal mass, and thus enables bettersplicing and alignment of ESIL 50 with optical fiber 54. Properalignment should position the center of the core of optical fiber 54 asclose as possible to second geometrical focus F₂. Optical fiber 54 canbe a single mode or multimode fiber. In this manner efficientin-coupling of collimated light 68 into fiber 54 as well as collimationof light exiting fiber 54 is achieved. The method of fusing fiber 54 toattachment surface portion 52 to obtain good alignment and reliablejoint 56 is known in the art. Further information on this technique canbe found in the patent references listed in the background section ofthis patent such as U.S. Pat. Nos. 4,962,988; 5,299,274. It should benoted that it is possible that attachment surface portion 52 forsplicing the ESIL 50 to waveguide 54 exhibit a mechanical feature, e.g.,a protrusion or circumferential ridge to further improve alignment.However, when using existing fusion splicing techniques it is preferablethat the attachment surface portion be substantially flat.

Since cross section 72 of pedestal 70 is substantially matched to crosssection 74 of optical fiber 54, existing fiber optic fusion splicingmethods using electric arc or laser heat sources can be used. Forexample, in some techniques for fusion splicing of single mode fibers,first the alignment is done by video camera keeping a small gap betweenthe fibers during heating by an electric arc, then the gap is closedonce the glass at the ends is heated just below the melting temperature.This method, as well as other methods may not require a gap toaccomplish uniform heating depending on the type of heat source used andhow the heat is supplied.

In a particular embodiment of ESIL 50 the material is fused silica witha refractive index of n=1.46 at a wavelength of 550 nm to match thefused silica of fiber 54 which has a refractive index of n=1.46 at 550nm as well. The total thickness of ESIL 50 is 2.5 mm. Pedestal 70 is 0.5mm long and has a diameter of 125 microns while body 62 has a diameterof 500 microns and is 2.0 mm long. The ellipsoidal eccentricitye=1/n=.6849; Major axis M=2.968 mm; separation between foci S=2.033 mmand the numerical aperture of ESIL 50 NA_(lens)=nsinq=0.146. The lastexceeds the numerical aperture of fiber 54 which is NA_(fiber)=0.13. Thebeam diameter of collimated light 68 is 0.446 nm. It will be appreciatedthat these values are merely exemplary of one particular design of ESIL50. For example, infrared wavelengths are used in telecommunicationssystems and require single mode optical fibers having a typical core of8 microns diameter and a cladding of 125 microns in diameter. Here, ESIL50 collimator design will be determined mainly by the desired diameterof collimated beam of light 68 and index of refraction n of the materialof ESIL 50 at the particular wavelength of operation.

FIG. 3B illustrates another embodiment of ESIL 50 collimator in whichlike reference numbers are used to designate corresponding parts fromFIG. 3A. In contrast to the embodiment of FIG. 3A, ESIL 50 has a taperedpedestal 80. In particular, a cross section 82 of pedestal 80 is matchedto the cross section of body 62 at bottom 64. The taper decreases fromthis larger cross section at bottom 64 to cross section 74 of fiber 54at attachment surface portion 52. In this embodiment ESIL 50 can also befabricated as one part or it can be made of two parts or sections, e.g.,body 62 and tapered pedestal 80 separately. The taper of pedestal 80enables good alignment and ensures reliable bonding with body 62. Infact, pedestal 80 could first be spliced with fiber 54 and then splicedor bonded by other means to body 62.

FIG. 3C illustrates an ESIL 100 collimator which is made of one section.ESIL 100 has an ellipsoidal surface portion 104 and cross section 102matched to cross section 74 of fiber 54. This permits splicing ESIL 100directly to fiber 54 without the use of pedestals. In this embodimentthe reduced cross section of ESIL 100 at ellipsoidal surface portion 104will reduce the collimated beam diameter of light 68.

FIG. 3D illustrates an ESIL 110 collimator attached to a waveguide 112buried in a structure 114. In this case, where the cross section of ESIL110 is substantially smaller than the cross section of structure 114 theattachment can be accomplished by a laser fusion splice method asdisclosed in U.S. Pat. No. 6,033,515, or by use of adhesives or othermethods.

FIG. 4 illustrates in a cross sectional side view of an optical system140 employing two ESIL collimators for use in a low-loss optical relayof diffraction-limited Gaussian beams.

The ESIL collimators 142 and 144 have similar properties to ESIL 12 ofFIG. 1. Single-mode waveguide 150 is attached to attachment surfaceportion 152 of ESIL 142. A Gaussian beam is shown propagating fromsingle-mode waveguide 150, through ESIL 142, and exiting the ellipsoidalsurface portion 143 as substantially collimated Gaussian beam 170.

ESIL 144 and single-mode waveguide 154 comprise the second half of theoptical relay. Substantially collimated Gaussian beam 170 is incident onESIL 144 at ellipsoidal surface portion 145 and focused to a Gaussianbeam waist substantially at point 162 on the attachment surface portion156 where it propagates through single-mode waveguide 154.

A person skilled in the art will recognize that a substantiallycollimated diffraction-limited Gaussian beam will experience diffractionspreading as it propagates away from the waist region. In this figurethe Gaussian beam waist region is located at 180. The Gaussian beamwaist diameter is defined as 2w_(o) where ω_(o) is the radius of theGaussian beam waist under consideration where the field amplitude of theintensity profile drops to {fraction (1/e)} of its peak value at thecenter of the beam. A further property of Gaussian beams is that as theinput spot w_(o)′ is made smaller, the beam expands more rapidly due todiffraction; remains collimated over a shorter distance in the nearfield; and diverges at a larger beam angle in the far field.

The distance a collimated Gaussian beam travels from the waist beforethe beam diameter increases by {square root over (2)} is denoted as the“Rayleigh Range” and defined as:$Z_{R} = \frac{{\pi\omega}_{o}^{2}}{\lambda}$

where λ is the wavelength of the beam in a vacuum.

Placing surface portion 152 at or near F₂ would result in a Gaussianbeam waist ω_(o) at or near the ellipsoidal surface portion 143 afterwhich point the beam would continually expand and diverge.

In the example shown, attachment surface portion 152 is offset from F₂,away from F₁, at a distance Z_(R)′. Z_(R)′ is the Rayleigh Range definedby the Gaussian beam waist ω_(o)′ at the interface between attachmentsurface portion 152 and waveguide 150. The Gaussian beam waist ω_(o)′ isdefined by the mode-field diameter 151 of waveguide 150. In the case oftelecom type single-mode optical fiber (e.g., Corning SMF-28) at awavelength of 1550 nm, the mode-field diameter is typically 25% largerthan its core diameter of 8 microns. Thus:$Z_{R}^{\prime} = \frac{{\pi\omega}_{o}^{\prime \quad 2}}{\frac{\lambda}{n}}$

where n is the index of refraction of ESIL 142 and λ is the wavelengthin vacuum.

As a specific example we will assume waveguide 150 is a Corning SMF-28fiber, which has a core diameter ≈8 μm and a mode-field diameter ≈10 μmTherefore ω_(o)′=5 μm, and if we assume a standard wavelength λ=1550 nm,and n=1.44 for ESIL 142, then Z_(R)′≈75 μm.

The previous example shows an optimized case for the described system.In this case, the second ellipsoidal surface portion 145 of ESIL 144placed at a distance 2Z_(R) will have the substantially collimatedGaussian beam 170 incident on ellipsoidal surface portion 145 having adiameter 146 of {square root over (2)}×2ω_(o)). Accordingly, a Gaussianbeam waist is formed at attachment surface portion 156 where itpropagates through single-mode waveguide 154.

FIG. 5 is an orthographic view of monolithic body 190 comprised ofsubstrate 192. Substrate 192 should have a substantially uniform indexof refraction n and could be made of silicon, zinc selenide, fusedsilica, moldable glass,plastic, or any other suitable optical material.

Multiple solid immersion lenses similar to SIL 194 form collimator array198 on the planar surface 196 of substrate 192. The SILs of collimatorarray 198 are integrated with substrate 192 of monolithic body 190.Prior art discusses how lenses can be formed from a monolithic bodyhaving a substrate with uniform index of refraction using processes suchas photolithography, etching, ion milling, reflowed photoresist methods,molding, and others.

The SILs of collimator array 198 could be formed with a variety ofsurface profiles including ellipsoidal or substantially ellipsoidalprofiles. A person skilled in the art will recognize that substantiallyellipsoidal profiles can be used when they satisfy the desired opticalperformance parameters. Alternatively, lens profiles such as spherical,hemispherical, aspherical, and others can also be used. Thus, acollimator array having a plurality of SILs arranged in a specificpattern, such as collimator array 198, can be used to provide aplurality of collimated beams from an optical waveguide array having aplurality of optical waveguides arranged in a matching pattern.

The SILs of collimator array 198 are preferably of the ESIL design asdescribed in FIGS. 1-4, and may be further arranged to form collimatorarray 198 in various configurations on planar surface 196 of monolithicbody 190. An example of an advantageous configuration would be toarrange multiple SILs to form a two-dimensional NxM matrix, where Nrepresents the number of rows of SILs, and M represents the number ofcolumns of SILs.

A specific example of an array configuration would comprise themonolithic body having an array comprised of 64 SILs arranged in an 8×8matrix. This monolithic body would have beneficial use in a low lossoptical relay for fiber optic applications such as in fiber opticswitches, Add/Drop multiplexers, wavelength multiplexers, wavelengthdemultiplexers, optical cross-connects, and other building blocks ofphotonic networks.

FIG. 6A illustrates a monolithic body 200 according to the inventionintegrating an array 213 of SIL 210 and SIL 212 with monolithic body 200on planar surfaces 201. Collimated Gaussian beams 199 pass through SIL210 and SIL 212 to focus at or near point 214 and point 216respectively. Parallel to planar surface portion 201 is surface portion270 passing through points 214 and 216. The monolithic body is comprisedof a substrate which should have a substantially uniform index ofrefraction. Waveguide 220 is attached to surface portion 270 atattachment surface portion 202 in alignment with focus 214. Waveguide222 is likewise attached to surface portion 270 at attachment surfaceportion 204 in alignment with focus 216. Possible methods of attachmentdiscussed in the prior art include laser fusion splicing and thermalbonding.

FIG. 6B illustrates another embodiment of monolithic body 200 in whichlike reference numbers are used to designate corresponding parts fromFIG. 6A. In contrast to the embodiment of FIG. 6A, monolithic body 200has the addition of cylindrical protrusions or pedestals 234 and 236extending from surface portion 270 with attachment surface portions 202and 204.

It is important that the region between monolithic body 200 andpedestals 234 and 236 preserve a uniform refractive index n. To ensurethis monolithic body 200 and pedestals 234 and 236 can be molded as onepart out of moldable glass or plastic or produced at the same time by aphotolithographic technique. For further information onphotolithographic and other fabrication techniques which can be used inthe manufacture of monolithic body 200, e.g., Optics & Photonics News,September 1999, pp. 19-22.

Pedestal 234 has a cross section 238 which substantially matches a crosssection 221 of optical fiber 220. This matching of cross sectionsenables better splicing and alignment of monolithic body 200 withoptical fiber 220. Proper alignment should position the center of thecore of optical fiber 220 as close as possible to the centerline of SIL210. Optical fiber 220 can be a single mode or multimode fiber. In thecase where optical fiber 220 is a single-mode fiber, then efficientin-coupling of collimated Gaussian beam 199 into fiber 220 as well ascollimation of light exiting fiber 220 is achieved. The method of fusingfiber 220 to attachment surface portion 202 to obtain good alignment anda reliable joint is known in the art. Further information on thistechnique can be found in the patent references listed in the backgroundsection of this patent such as U.S. Pat. Nos. 4,962,988; 5,299,274;4,737,006; 6,033,515. It should be noted that it is possible thatattachment surface portion 202 for splicing the monolithic body 200 towaveguide 220 exhibit a mechanical feature, e.g., a protrusion orcircumferential ridge to further improve alignment. However, when usingexisting fusion splicing techniques it is preferable that the attachmentsurface portion be substantially flat.

Since cross section 238 of pedestal 234 is substantially matched tocross section 221 of optical fiber 220, existing fiber optic fusionsplicing methods using electric arc or laser heat sources can be used.For example, in some techniques for fusion splicing of single modefibers, first the alignment is done by video camera keeping a small gapbetween the fibers during heating by an electric arc, then the gap isclosed once the glass at the ends is heated just below the meltingtemperature. This method, as well as other methods may not require a gapto accomplish uniform heating depending on the type of heat source usedand how the heat is supplied.

FIG. 6C illustrates a further embodiment of monolithic part 200illustrated in FIG. 6A. In contrast to the embodiment of FIG. 6B,monolithic body 200 has tapered pedestals 260 and 262. In particular, across section 264 of pedestal 260 is larger than cross section 221 ofwaveguide 220 at attachment surface portion 266. The taper decreasesfrom a larger cross section at surface portion 270 to cross section 221of fiber 220 at attachment surface portion 266. In this embodimentmonolithic body 200 can also be fabricated as one part or it can be madeof two parts or sections, e.g., monolithic body 200 and tapered pedestal260 separately. The taper of pedestal 260 enables good alignment andensures reliable bonding with body 200. In fact, pedestal 260 couldfirst be spliced with fiber 220 and then spliced or bonded by othermeans to monolithic body 200.

FIG. 6D illustrates a monolithic body 200 attached to a waveguide 284buried in a structure 282. In this case, where the cross section ofmonolithic body 200 is substantially smaller than the cross section ofstructure 282 the attachment can be accomplished by a laser fusionsplice method as disclosed in U.S. Pat. No. 6,033,515, or by use ofadhesives or other bonding methods.

Illustrated in FIG. 7A is monolithic body 300 similar to that describedin FIGS. 6A-D. Pedestals 306 and 308 are integrated with monolithic body300 on surface portion 302. Waveguides 310 and 312 are attached topedestals 306 and 308 respectively. In instances where waveguides 310and 312 may be very fragile (e.g., single-mode optical fibers typicallyhave a cladding diameter of 125 microns and a core diameter of 8microns), then a reinforcing structure may be required to prevent afailure. Supporting the attachment of waveguide 310 to pedestal 306 isreinforcing structure 316. Reinforcing structure 316 is in contact withwaveguide 310 along surface 318 and is attached at joint 320.Reinforcement structure 316 is also attached to monolithic body 300 atjoint 322. In this embodiment, the reinforcing structure is shown as ahollow tubular member. A person skilled in the art will recognize thatthe material chosen for the reinforcing structure is a matter of designpreference. This material may be comprised of glass, plastic, metal,silicon, or a variety of other suitable options. The method ofattachment of reinforcing structure 316 to waveguide 310 and monolithicbody 300 will be determined by the materials chosen. Prior art discusseshow this attachment can be made using adhesives and thermal bondingprocesses such as soldering or thermal-anodic bonding methods.

It should be recognized by one skilled in the art that reinforcingstructure 316 not only supports the attachment of waveguide 310 tomonolithic body 300, an appropriate bonding material at attachmentjoints 320 and 322 will also absorb stress and strain put on the system,thus making the system more robust and stable.

FIG. 7B illustrates a further embodiment of FIG. 7A. In contrast totubular reinforcing structure 316 of FIG. 7A, the reinforcing structurecomprises block 330 having hollowed portions 332 and 334 to accommodatewaveguides. Block 330 is attached to waveguides 310 and 312 at joints336, and to monolithic body 300 at joints 338.

The above embodiments are presented to illustrate the present inventionand are not to be construed as limitations thereof. Accordingly, thescope of the invention should be determined by the following claims andtheir legal equivalents:

What is claimed is:
 1. A collimator integrated with a waveguide, saidcolimator comprising: a) an ellipsoidal solid immersion lens having asubstantially uniform index of refraction n, an ellipsoidal surfaceportion defining a geometrical ellipsoid having a major axis of lengthM, a first geometrical focus F₁, a second geometrical focus F₂ separatedfrom said first geometrical focus F₁ by a separation S=M/n; and b) anattachment surface portion passing substantially through said secondgeometrical focus F₂ for attachment said ellipsoidal solid immersionlens to said waveguide such that a substantially collimated light beamexhibiting a Gaussian type intensity profile propagating along saidmajor axis M through said ellipsoidal surface portion converges to aGaussian beam waist substantially at said attachment surface portion. 2.The collimator of claim 1, wherein said attachment surface portionpasses through said geometric focus F₂ at an offset no greater than thecorresponding Rayleigh Range of said Gaussian beam waist.
 3. Thecollimator of claim 1, wherein said attachment surface portion passesthrough said geometric focus F₂ at an offset no greater than 75 microns.4. The collimator of claim 1, wherein said attachment surface portion isattached to said waveguide by a fused butt joint.
 5. The collimator ofclaim 1, wherein said waveguide is selected from the group consisting ofoptical fibers and buried waveguides.
 6. The collimator of claim 1,wherein said ellipsoidal solid immersion lens comprises a bodycomprising said ellipsoidal surface portion and a pedestal comprisingsaid attachment surface portion.
 7. The collimator of claim 6, whereinsaid pedestal has a pedestal cross section substantially matched to saidwaveguide.
 8. The collimator of claim 7, wherein said waveguide is anoptical fiber.
 9. The collimator of claim 6, wherein said pedestal has atapered pedestal cross section.
 10. The collimator of claim 1, whereinsaid ellipsoidal solid immersion lens has a cross section substantiallymatched to said waveguide.
 11. The collimator of claim 10, wherein saidwaveguide is an optical fiber.
 12. The collimator of claim 1, whereinsaid ellipsoidal solid immersion lens comprises at least two sections.13. The collimator of claim 1, wherein said attachment surface portionis substantially flat.
 14. The collimator of claim 1, wherein saidwaveguide is a single mode optical fiber.
 15. The collimator of claim14, wherein said ellipsoidal solid immersion lens is made of a materialfrom the group consisting of fused silica and moldable glass.
 16. Thecollimator of claim 1, wherein said attachment surface portion isattached to said waveguide by an adhesive.
 17. The collimator of claim1, wherein said attachment surface portion is attached to said waveguideby a laser fusion-splice.
 18. The collimator of claim 1, wherein saidattachment of said ellipsoidal solid immersion lens to said waveguide issupported by a reinforcing structure.
 19. The collimator of claim 18,wherein said reinforcing structure comprises a hollow tube.
 20. Thecollimator of claim 18, wherein said reinforcing structure comprises areinforcement block having a hollow portion.
 21. The collimator of claim18, wherein said reinforcing structure is attached to said waveguide.22. The collimator of claim 21, wherein said reinforcing structure isattached to said waveguide by a bond from the group consisting ofadhesive bonds and thermal bonds.
 23. The collimator of claim 18,wherein said reinforcing structure is attached to said ellipsoidal solidimmersion lens.
 24. The collimator of claim 23, wherein said reinforcingstructure is attached to said ellipsoidal solid immersion lens by a bondfrom the group consisting of adhesives and thermal bonding.
 25. Acollimator array comprising at least one collimator of claim
 1. 26. Acollimator array integrated with a waveguide array having a plurality ofwaveguides, said collimator array comprising: a monolithic bodycomprising: a substrate having a substantially uniform index ofrefraction n; a lens array having a plurality of solid immersion lenses;and a plurality of pedestals comprising a plurality of attachmentsurface portions for attaching said solid immersion lenses to saidplurality of waveguides.
 27. The collimator array of claim 26, whereinsaid solid immersion lenses are ellipsoidal solid immersion lenses,wherein each of said ellipsoidal solid immersion lenses comprises: a) anellipsoidal surface portion defining a geometrical ellipsoid having amajor axis of length M, a first geometrical focus F₁, a secondgeometrical focus F₂ separated from said first geometrical focus F₁ by aseparation S=M/n; and b) an attachment surface portion passingsubstantially through said second geometrical focus F₂ for attachingsaid ellipsoidal solid immersion lens to said waveguide such that asubstantially collimated light beam exhibiting a Gaussian type intensityprofile propagating along said major axis M through said ellipsoidalsurface portion converges to a Gaussian beam waist substantially at saidattachment surface portion.
 28. The collimator array of claim 26,wherein said attachment surface portions are attached to said waveguidesby fused butt joints.
 29. The collimator array of claim 26, wherein saidwaveguides are selected from the group consisting of optical fibers andburied waveguides.
 30. The collimator array of claim 26, wherein saidpedestals have a pedestal cross section substantially matched to saidwaveguides.
 31. The collimator array of claim 30, wherein saidwaveguides are optical fibers.
 32. The collimator array of claim 26,wherein said pedestals have a tapered pedestal cross section.
 33. Thecollimator array of claim 26, wherein said attachment surface portionsare substantially flat.
 34. The collimator array of claim 26, whereinsaid waveguides are single mode optical fibers.
 35. The collimator arrayof claim 34, wherein said substrate comprises a material from the groupconsisting of fused silica and moldable glass.
 36. The collimator arrayof claim 26, wherein said attachment surface portions are attached tosaid waveguides by a means from the group consisting of adhesives andlaser fusion-splicing.
 37. The collimator array of claim 26, whereinsaid attachment of said monolithic body to said waveguides is supportedby a reinforcing structure.
 38. The collimator array of claim 37,wherein said reinforcing structure comprises a plurality of hollowtubes.
 39. The collimator array of claim 37, wherein said reinforcingstructure comprises a reinforcement block having a plurality of hollowportions.
 40. The collimator array of claim 37, wherein said reinforcingstructure is attached to said waveguides.
 41. The collimator array ofclaim 40, wherein said reinforcing structure is attached to saidwaveguides by a means from the group of adhesive bonds and thermalbonds.
 42. The collimator array of claim 37, wherein said reinforcingstructure is attached to said monolithic body.
 43. The collimator arrayof claim 42, wherein said reinforcing structure is attached to saidmonolithic body by a means from the group consisting of adhesive bondsand thermal bonds.
 44. The collimator array of claim 26, wherein saidlens array comprises a pattern of said plurality of solid immersionlenses.
 45. The collimator array of claim 26, wherein said lens arraycomprises a one-dimensional matrix of said plurality of solid immersionlenses.
 46. The collimator array of claim 26, wherein said lens arraycomprises a two-dimensional matrix of said plurality of solid immersionlenses.
 47. The collimator array of claim 26, wherein said lens array isformed by at least one processing method chosen from the groupconsisting of etching, ion milling, molding, reflowed photoresistprocesses and photolithography.
 48. The collimator array of claim 26,wherein said monolithic body is comprised of a material from the groupconsisting of fused silica, moldable glass, and silicon.
 49. Acollimator integrated with a waveguide, said collimator comprising: a)an ellipsoidal solid immersion lens having a substantially uniform indexof refraction n, an ellipsoidal surface portion defining a geometricalellipsoid having an eccentricity e=1/n; b) an attachment surface forattaching said ellipsoidal solid immersion lens to said waveguide suchthat a substantially collimated light beam exhibiting a Gaussian typeintensity profile propagating along a major axis M of said ellipsoidalsolid immersion lens through said ellipsoidal surface portion convergesto a Gaussian beam waist substantially at said attachment surfaceportion.
 50. An optical relay for propagation of a light beam from afirst single-mode waveguide to a second single-mode waveguide, saidoptical relay comprising: a) a first solid immersion lens having a firstsubstantially uniform index of refraction n, a first substantiallyellipsoidal surface portion substantially defining a first geometricalellipsoid having first and second foci F₁ and F₂, and eccentricitye=1/n, and a first attachment surface portion passing substantiallythrough the second focus F₂ for attaching said first solid immersionlens to said first single-mode waveguide; and b) a second solidimmersion lens having a second substantially uniform index of refractionn', a second substantially ellipsoidal surface portion substantiallydefining a second geometrical, ellipsoid having first and second fociF₁'and F₂', and eccentricity e'=1/n', and a second attachment surfaceportion passing substantially through the second focus F₂'for attachingsaid second solid immersion lens to said second single-mode waveguide,wherein, said light beam propagates from said first single-modewaveguide through said first solid immersion lens such that said lightbeam exits said first substantially ellipsoidal surface portion of saidfirst solid immersion lens as a substantially collimated beam, andwherein said first and second solid immersion lenses are spaced apartsuch that said substantially collimated beam is incident on said secondsubstantially ellipsoidal surface portion of said second solid immersionlens, whereby said light beam is substantially focused on said secondattachment surface portion of said second solid immersion lens such thatat least a portion of said light beam propagates through said secondsingle-mode waveguide.
 51. The optical relay of claim 50, wherein saidfirst and said second geometrical ellipsoids have substantially the sameeccentricity.
 52. The optical relay of claim 50, wherein said firstattachment surface portion is attached to said first single-modewaveguide by a fused butt joint.
 53. The optical relay of claim 50,wherein said second attachment surface portion is attached to saidsecond single-mode waveguide by a fused butt joint.
 54. The opticalrelay of claim 50, wherein at least one of said first and secondsingle-mode waveguides are selected from the group consisting ofsingle-mode optical fibers and single-mode buried waveguides.
 55. Theoptical relay of claim 50, wherein said first solid immersion lenscomprises a body comprising said first substantially ellipsoidal surfaceportion and a pedestal comprising said first attachment surface portion.56. The optical relay of claim 55, wherein said pedestal has a pedestalcross section substantially matched to said first single-mode waveguide.57. The optical relay of claim 56, wherein said first single-modewaveguide is a single-mode optical fiber.
 58. The optical relay of claim55, wherein said pedestal has a tapered pedestal cross section.
 59. Theoptical relay of claim 50, wherein said second solid immersion lenscomprises a body comprising said second substantially ellipsoidalsurface portion and a pedestal comprising said second attachmentsurfaces portion.
 60. The optical relay of claim 59, wherein saidpedestal has a pedestal cross section substantially matched to saidsecond single-mode waveguide.
 61. The optical relay of claim 60, whereinsaid second single-mode waveguide is a single-mode optical fiber. 62.The optical relay of claim 59, wherein said pedestal has a taperedpedestal cross section.
 63. The optical relay of claim 50, wherein saidfirst solid immersion lens has a cross section substantially matched tosaid first single-mode waveguide.
 64. The optical relay of claim 63,wherein said first single-mode waveguide is a single-mode optical fiber.65. The optical relay of claim 50, wherein said second solid immersionlens has a cross section substantially matched to said secondsingle-mode waveguide.
 66. The optical delay of claim 65, wherein saidsecond single-mode waveguide is a single-mode optical fiber.
 67. Theoptical relay of claim 50, wherein at least one of said first and secondsolid immersion lenses comprises at least two sections.
 68. The opticalrelay of claim 50, wherein at least one of said first and secondattachment surface portions is substantially flat.
 69. The optical relayof claim 50, wherein at least one of said first and second single-modewaveguides is a single-mode optical fiber.
 70. The optical relay ofclaim 50, wherein at least one of said first and second solid immersionlenses is made of a material from the group consisting of fused silicaand moldable glass.
 71. The optical relay of claim 50, wherein saidfirst attachment surface portion is attached to said first single-modewaveguide by a bond selected from the group consisting of adhesive bondsand laser fusion-splices.
 72. The optical relay of claim 50, whereinsaid second attachment surface portion is attached to said secondsingle-mode waveguide by a bond selected from the group consisting ofadhesive bonds and laser fusion-splices.
 73. The optical relay of claim50, wherein said first attachment surface portion is attached to saidfirst single-mode waveguide by a laser fusion-splice.
 74. The opticalrelay of claim 50, wherein said attachment of said first solid immersionlens to said first single-mode waveguide is supported by a reinforcingstructure.
 75. The optical relay of claim 74, wherein said reinforcingstructure comprises a hollow tube.
 76. The optical relay of claim 74,wherein said reinforcing structure comprises a reinforcement blockhaving a hollow portion.
 77. The optical relay of claim 74, wherein saidreinforcing structure is attached to said first single-mode waveguide.78. The optical relay of claim 77, wherein said reinforcing structure isattached to said first single-mode waveguide by a bond selected from thegroup consisting of adhesive bonds and thermal bonds.
 79. The opticalrelay of claim 74, wherein said reinforcing structure is attached tosaid first solid immersion lens.
 80. The optical relay of claim 79,wherein said reinforcing structure is attached to said first solidimmersion lens by a bond selected from the group consisting of adhesivebonds and thermal bonds.
 81. The optical relay of claim 50, wherein saidattachment of said second solid immersion lens to said secondsingle-mode waveguide is supported by a reinforcing structure.
 82. Theoptical relay of claim 81, wherein said reinforcing structure comprisesa hollow tube.
 83. The optical relay of claim 81, wherein saidreinforcing structure comprises a reinforcement block having a hollowportion.
 84. The optical relay of claim 81, wherein said reinforcingstructure is attached to said second single-mode waveguide.
 85. Theoptical relay of claim 81, wherein said reinforcing structure isattached to said second single-mode waveguide by a bond selected fromthe group consisting of adhesive bonds and thermal bonds.
 86. Theoptical relay of claim 81, wherein said reinforcing structure isattached to said second solid immersion lens.
 87. The optical relay ofclaim 86, wherein said reinforcing structure is attached to said secondsolid immersion lens by a bond from the group consisting of adhesivebonds and thermal bonds.